1. Field of Invention
This invention relates to a method of dicing a wafer. More particularly, the present invention is related to a method of dicing a wafer with a removable layer formed thereon for reducing the stress at the wafer so as to prevent the wafer from chipping when the singulating process is performed to dice the wafer.
2. Related Art
In this information explosion age, integrated circuits products are used almost everywhere in our daily life. As fabricating technique continue to improve, electronic products having powerful functions, personalized performance and a higher degree of complexity are produced. Nowadays, most electronic products are relatively light and have a compact body. Hence, in semiconductor production, various types of high-density semiconductor packages have been developed. Flip chip is one of the most commonly used techniques for forming an integrated circuits package. Moreover, compared with a wire-bonding package or a tape automated bonding (TAB) package, a flip-chip package uses a shorter electrical path on average and has a better overall electrical performance. In a flip-chip package, the bonding pads on a chip and the contacts on a substrate are connected together through a plurality of bumps formed on the chip by a conventional bumping process and then an underfill material is filled into the gap between the chip and the substrate to encapsulate the bumps so as to well protect the bumps. In such a manner, the reliability of such flip chip package is enhanced.
As mentioned above, in a conventional assembly packaging process, there is provided a wafer with a back surface and a sawing tape formed on said back surface to fix the wafer onto a carrier for proceeding the process of dicing or singulating the wafer. Afterwards, the wafer is sawed by a blade sawing along the cutting lines on the active surface of the wafer so as to form a plurality of separate chips attached on the sawing tape. However, usually the sawing tape is securely attached to the back surface of the wafer so that it is not easy to remove the separate chips from the sawing tape. In addition, when the sawing blade cuts the wafer along the cutting lines, the blade usually not only cuts the wafer but also the sawing tape. To be noted, the sawing tape is partially cut. Besides, the stress caused by the sawing blade cutting the wafer is transferred to and concentrated at the back surface of the wafer so as to cause the back surface of the wafer to be chipping.
As disclosed in U.S. Pat. No. 6,264,535, there is disclosed a method of singulating a wafer for preventing the back surface of the wafer from chipping. Therein, firstly, there is provided a first tape attached to the back surface of the wafer and then a singulating process is performed to partially cut the wafer to form a partially separated wafer. Next, there is provided a second tape on the active surface of the partially separated wafer, namely, the second tape is disposed on the active surfaces of the partially separated wafer. Then, the first tape is removed from the back surface of the partially separated wafer and then a grinding process is performed on the back surface of the partially separated wafer until a plurality of individual chips are formed on the second tape. Next, a third tape is provided on the back surfaces of the individual chips and then the second tape is removed so as to perform the processes of picking and placing. However, as it can be seen, there are a lot of tapes wasted and it is easy to cause the wafer damaged. Frankly speaking, chipping is usually found at the edge of the back surface of the wafer. In other words, when the blade cuts the sawing tape at a cutting depth much smaller than the thickness of the sawing tape, namely, the un-cutting portion is close to the interface of the back surface of the wafer and the sawing tape, it is easy to cause the wafer to be chipping.
Furthermore, another singulating process is disclosed in U.S. Pat. No. 6,175,162. Therein, a protective film is provided on the back surface of the wafer for regarding as a buffer layer to prevent the wafer from being chipping. However, the protective film is still left on the back surfaces of the individual chips so as to lower the thermal reliability of the individual chips. In addition, such protective film has a higher glutinosity, so it is not easy to separate the wafer into a plurality of individual chips.
Therefore, providing another dicing method to solve the mentioned-above disadvantages is the most important task in this invention.